Fluxes are applied to weld joints in several forms to create slag that protects the molten weld metal from ambient conditions as the weld cools. In general, the welding flux solidifies after the weld to form a protective slag over on top of the weld. Once the weld cools, the slag is chipped off or otherwise removed. Several common methods of providing flux to a welding operation exist. One technique involves performing the weld within a pile of granular flux (e.g., submerged arc welding (SAW) processes). Another common type of arc welding operation is shielded metal arc welding (SMAW) (e.g., also known as stick welding or manual metal arc welding), in which the solid welding electrode is coated with a flux material that forms the protective slag. Gas metal arc welding (GMAW) or metal inert gas (MIG) welding involves the use of shielding gas commonly provided from an external source to protect the weld process including the arc and the weld metal from ambient effects such as oxidation and/or nitridation, wherein the flux may be provided in the interior of a cored electrode structure (e.g., flux cored arc welding or FCAW), or the electrode may be coated with flux material. In welding operations generally, the slag is removed following creation of the weld joint, wherein it is desirable to provide welding flux that produces slag which is easily removed without damage to the weld joint or to the workpiece.
In the case of submerged arc welding, a bare welding electrode is fed into a workpiece weld groove, where the point of metal fusion and the arc are submerged within a separate flux in order to shield the arc from the ambient environment of the welding operation. The molten weld pool and the arc zone are thus protected from atmospheric contamination by being submerged in the flux. Submerged arc welding has many advantages, including high deposition rates, deep weld penetration, high weld quality, and high lineal welding speeds for thin sheet steel workpieces with minimal welding fume or arc light emission. Submerged arc welding typically uses a relatively large diameter electrode that is fed through the pile of granular flux and into the arc at a controlled rate. The arc is shielded by a granular flux which is poured to form a pile in and sometimes over a weld groove of the workpiece being welded so as to surround the arc. Submerged arc welding is often used for high quality applications, such as welding deep groove joints, wherein multiple welding passes are performed to join two workpiece edges together. For deep groove welding, several weld passes are performed, with an initial pass being formed at the bottom of the joint groove, followed by one or more subsequent welds to join the workpiece edges, eventually filling the groove with metal.
In each pass, the welding flux or gas operates to prevent oxygen or other ambient impurities from reacting with the weld metal (e.g., oxidation), and some of the molten flux is converted to slag by the arc. The slag then solidifies and helps to protect the weld as it cools. Although the slag is a helpful byproduct of SAW processes for protection during weld cooling, the slag must be removed before beginning the next pass in a multiple pass welding process to maintain high weld quality. The same is true of FCAW, SMAW, and GMAW processes generally, wherein the ability to easily remove remnant slag following a welding operation is a desirable performance characteristic for welding flux, regardless of the way in which the flux is provided to the process. If any slag remains in the weld groove when a new pass begins, slag inclusions may result, which are elongated or globular pockets of metallic oxides, electrode coating materials, resolidified flux and/or other solid compounds within a cooled weld joint that may be subject to fracturing or cracking over time or may otherwise degrade the quality of the finished weld joint. In multilayer welding operations, such slag inclusions can be avoided or mitigated by preparing the groove and weld properly before each bead or new pass is deposited, removing all slag before beginning a new pass by chipping, chiseling, and/or other cleaning operations, and by ensuring that the slag rises to the surface of the weld pool during each welding pass by avoiding low lineal travel speeds and low currents.
In deep groove welding operations, moreover, it is generally desirable to minimize the joint groove angle, so as to conserve welding consumables and to minimize welding times. However, as the groove angle decreases for a given groove depth (e.g., narrow gap deep groove multi-pass welding operations), cleaning the excess slag and ensuring that the molten flux rises to the top of the weld puddle is increasingly difficult, particularly for the initial or root pass at the bottom of the joint groove. In this regard, different granular fluxes perform differently with respect to ease of removal from narrow workpiece grooves, and welding system operators need to know which flux to employ in a given operation. Accordingly, there is a need for techniques by which welding consumables, including granular fluxes for SAW applications and fluxes provided within or on an outer surface of welding electrodes in other types of welding processes can be analyzed and compared for deciding which consumable to use in a given narrow gap deep groove welding operation.